In a polishing apparatus for wafers such as silicon wafers, it is general to stop a turntable or a machining head of a rotary system in a standby state where a wafer is not polished. Further, it is also general to keep a turntable cooling function in the same state as that in polishing even in the standby state, and to intermittently supply a water retaining liquid to a polishing pad to prevent the polishing pad attached to an upper side of the turntable from being dried.
The polishing apparatus for semiconductor wafers is mainly constituted of a polishing stage having a turntable which carries out polishing and a conveying stage which conveys wafers. In the wafer conveying stage, ejection of each wafer from a cassette, storage of the wafer in the cassette, and attachment/detachment of the wafer to/from holding means such as a polishing head are performed. It is to be noted that this series of operations are all completed within a polishing time.
In the polishing stage, a wafer held by the polishing head is brought into contact with the polishing pad while supplying a polishing agent onto the polishing pad attached to the turntable, and the polishing head and the turntable are rotated to perform the polishing. At the time of the polishing, heat is generated due to friction of the polishing pad, the polishing agent, and the wafer, or heat is generated from a motor by rotation of the turntable.
As to the heat generation due to the friction during the polishing, for the purpose of maintaining a temperature of the turntable constant, a refrigerant such as low-temperature cooling water is flowed to a turntable unit to remove the heat (see Patent Literature 1). Further, as to the heat generation from the motor, a motor peripheral portion is cooled by the low-temperature cooling water or forced exhaust is performed at a position where the motor is installed to prevent a turntable temperature from increasing beyond necessity.
In a heat removal operation for such heat generation, a water temperature and a water amount of cooling water or the like and an exhaust amount are adjusted so that an effect can be exerted even in a state where heat generation is considerable at the time of the polishing. Further, in the heat removal operation, the cooling water is constantly supplied to the turntable unit irrespective of the machining state or the standby state, and supply of the cooling water or forced exhaust is also constantly performed in the motor unit.
Thus, in the turntable which is in the standby state where the polishing is not performed, a turntable temperature is lowered approximately 2.17% as compared with that in the polishing. When a next water is polished in a state where the turntable temperature is low, a stock removal or a wafer shape differs from that in previous polishing in an early stage of restart of machining. Moreover, in the state where the turntable temperature is low, the stock removal of polishing is reduced or variations in flatness increase. Thus, when the turntable temperature is lowered in the standby state, a warm-up operation based on polishing of a dummy wafer is performed before polishing a subsequent wafer, and thereafter the subsequent wafer is polished.